dns server

they should tell u themselves or if ur running winowds xp go to control panel network connections right click on the one ur using click status, then on status screen click support and then details and it should be there.

dns (domian name system)your isp provides this so when you look uo web pages using names it translates it into ip addresses.There could number of reasons for this .Best bet to call your isp and tell them YOU cannot access the internet.